Calculator blog

We have just been informed that the repair kits are ready for shipment. We have a limited supply, and some of our customers that asked to be informed of the arrival of the kits have already placed an order for it.

But as the number of units is relatively low, you would better place the order soon.

Regarding installation, I have learned several tricks the hard way:

• It is extremely important to file away all the rest of the rivets from the original film. If not, it won’t adhere well.
• In order to do a proper bending, you need to punch little holes in the non-copper parts of the film.
• If at all possible, do the “cooking” suggested in the manual
• Patience, patience…

There is a very well known word problem that appeared first in the seminal article “mathematics written in sand”, by .

In short, the problem was defined as:

“A bank retains a legal consultant whose thoughts are so valuable that she is paid for them at the rate of a penny per second, day and night. Lest the sound of pennies dropping distract her, they they are deposited into her account to accrete with interest at the rate of 10% per annum compounded every second. How much will have accumulated after a year (365 days) ?

Enter data:

n := 606024*365 = 31,536,000 sec. per year.

i := 10/n = 0.000 000 317 097 9198 % per sec.

PV:= 0

PMT := –0.01 = one cent per sec. to the bank.”

This problem implies so many decimals and so many compounded periods that the issue here is one of accuracy - and the difference between several calculators can be astounding!

Let’s see the result in several calculators:

Real solution:

HP41c, TVM program, advantage pac: 331.667,0067

HP17bII+: 33.667,006691

HP19bII

HP50g: 33.667,006691

HP Prime: 331.667,006691

Next time I’ll find the result in Texas Instruments calculators…

To do list for this week:

check the workings of Streamsmart 410 (I have now noticed that I have written in our website smart stream repeatedly all around) together with the HP Prime - use as many probes as possible.

check the workings of Streamsmart 410, but now using the old -and soon to be discontinued - hp50g.

Compare both implementations from a student point of view and from a scientific point of view. See which is the real maximum sampling rate in both cases. See what is the accuracy in both systems.

In fact, let’s see which is the better of the two.

As engineer by training (but not trade), I want a calculator that can do anything an engineer may do - but I have not been interested in heavy mathematics - at least while my children were in primary school. I have to admit that I often get the results that I want sooner when I do them myself than when I get the calculator to solve the equation in my stead. So I have been using scientific calculators preferentially over graphical ones - basically I have never needed to plot anything on a calculator ever. I have needed to plot formulae on paper, for presentation purposes, but what’s the point of doing it in a calculator if you can’t share it?

Now, if you think about it, a graphical calculators has some advantages over a scientific one. For one, you can see several previous results on screen - instead of one or two lines at best. What is more, it can evaluate expressions that you would need to write a solve formula for, in a more cumbersome way in a scientific calculator. The only comparable way of doing it was the solver used in the HP17bII and HP19bII calculators. But in addition, the graphical calculator has (or can have) CAS: computer algebra system.

Computer-assisted Algebra calculators have been for a long time among us, basically from the HP28c from 1986. It took much longer to TI to come up with something similar, in 1995 - but they have taken the whole market by storm, by concentrating on the student market instead of the engineering market. HP concentrated on the latter - and eventually lost both! Let’s hope that the current intent with the Prime can recover part of it. It will only happen if HP wholeheartedly supports it with all their means - and add the areas where HP can make a difference: communications and measuring.

When using the prime for business I only work in the Home area; basically because it’s the only area where I can work in RPN; but more and more I am using the CAS environment when the function I want to use doesn’t appear in the Home environment. And it is good to have two calculators at the press of a key: a RPN (Home) and algebraic with CAS (CAS). You will see several posts on CAS from now one - but I need to refresh a lot of the concepts I learned on the introductory engineering courses.

One thing that I have seen missing in the Prime firmware is the “step by step” configuration that can be found in the HP50g. For example, when you want to diagonalize a matrix, it is good to see what you’re doing. But let’s not advance ourselves as we learn the machine!

I have taken some multimeters for revision to the persone that does the repairs for us. In this case, there were a Hp3468A and a HP3478A.

Both were quite similar functionally. a general multimeter with voltage, current and resistance meters. The main difference were the interfaces.

The HP3478A was desk-based, sporting a HP-IB interface, able to be connected to HP computers like the HP85 (with which I am still using it)

The HP3468A was intended to be carried with you, and it had an HP-IL interface, to be used with handhelds like the HP41c and the HP71b. This is the one that I am using on my desk when repairing units.

Tomorrow I will tell you about the conversation with Ignacio, the person that does our repairs. He is a true fanatic of HP calculators. He has several units of nearly all models. For example, he must have around 10 HP41 units of all types, but he won’t part with any of them! Jokingly, I told him that he couldn’t have created Apple, for Steve Wozniak had to sell his HP65 to buy parts for the Apple 1

I have put on sale too a set of Goertz Python cables, 2.6 meters in length. These have a very peculiar geometry: there are 4 flat copper strips, intimately put one on top of the other, with a very thin coat of high grade (teflon) dielectric between, twisted along its length at a rate of aproximately 1,5 turns per feet, and then covered by other dielectric to make it cylindric. It has the same electrical properties of the fleet Goetz MI2.

What is this geometry for?. Typically, you are feeding a loudspeaker from an amplifier that has an output impedance below 1 ohm, and in many cases much lower than that. It is then used to feed a loudspeaker that has an average impedance between 4 and 8 ohms.

Now, the typical speaker cable characteristic impedance is between 50 and 200 ohm. This implies huge mismatches, which in turn cause signal reflections at the cable ends, which imply rounding of waveforms and worse treble performance. On the other hand a low characteristic impedance is better to maximize the power transfer - something that is required with high power amplifiers and demanding speakers.

The geometry dictates the characteristic impedance, through the relation between inductance and capacitance, which in turn gives the characteristic impedance: Z_0 = sqrt(L/C). As this cable has very low inductance (both cables are very much together, with very small area between them) and high capacitance (it looks like an unrolled capacitor). As a consequence, it is the best cable I have used so far. I am using it with a Devialet D200 amplifier, driving a couple of Gallo Stradas loudspeaker.

I have not posted pictures yet, since I still have them connected to my amp and speakers.

Why am I selling it? Because I have a roll of Goertz MI2 flat cable, which I have used to produce a shorter run of speaker cable that I have subsequently sent to deep cryogenic treatment, in a company specialized in doing so for razing car applications, but that is also used by a couple of audio companies to treat their cables. Stay tuned to hear about its performance when they come back!

You know that my other hobby is music and hi-fi. I have quite a good system, but I spend too much time tweaking it to get the best possible sound.

Most of my customers are engineers - or at least engineer driven.

Living in a family, listening to music is hampered by the fact that you can’t play music as frequently as you want, as loud as you want it. As I work most of the week in Norway, far from my family, I have that part covered. I typically listen to music, in the sweet spot in front of the loudspeakers, for 5 hours every day.

But when I am back in Barcelona or in our mountain den, then it has to be headphones.

In Barcelona I use a Benchmark DAC1 Pre - a 6 year old machine, that was a Stereophile class A product at its time, together with a Sennheiser 800 headphone - a machine that appears in all 10-best lists, anywhere. I even upgraded the cable to a Cardas model, to tame a little bit the treble.

Lately I have put together in the mountain den a system based on a Linn Classic Movie Di, a Woo Wee electrostatic energizer and a Stax 404 electrostatic ear speaker (as Stax calls them). It is fed from its own CD player, but also through Toslink from an apple TV, being fed from my computer through airplay. Despite being old equipment (everything at least 8 years old, except the Woo Wee energizer). I was surprised by the sheer quality of the sound - much better than that of the Sennheiser! And for a fraction of the price.

So much so that I have taken out from stock an old Stax Lambda Pro ear speaker, together with a humble SRS–252s electrostatic amplifier (the lowest in level from Stax). This is fed from a Meridian Explorer DAC, first version, from my mac too. It is amazing! The lowest level, 20 years old technology from Stax, beats handily the mighty Sennheiser HD800 - admittedly one of the best headphones in the world - see http://www.innerfidelity.com/content/innerfidelitys-wall-fame-full-size-open.

Does anyone want a second hand Sennheiser HD800? If so, please drop me a line at jose@thecalculatorstore.com.

You can see the current audio offers in the audio page.

I guess that I will include more Sta products in the audio zone.

These days we have changed our web server. This was the reason that we had the website down for half a day during the morning of last Wednesday. I hope that the increase speed can provide a better site navigation. I also apologize in case you wanted to enter and could not do it.

Coming back to business: I have received a mail from the friends at Swissmicro.com, the ones that provided the credit card-sized HP15c. I have a couple of units of an early version; later versions were much better made and good looking.

The message was to announce the creation of the HP41c in exactly the same format. It can use alphanumerics, comes with a proper clock (so you don’t need the time module - it is included) and it even has overlays for stopwatch and others. I look forward to get some units. You can find it here:

www.swissmicros.com

We have heard from the producer that we will receive the next batch of repair packs for the HP41c battery bay will arrive mid November. The designer and producer ended the last batch some time ago, and ordered another.

You can bet that order sizes are small, and priority chez the factory is low. There are not too many users willing to repair their HP41c. Most of them don't know that a proper solution exists for their crippled calculators.

Also, there are only 4 units left worldwide of CL circuits of the latest version (v4): Monte has 3, and I have one. It is already installed in a wonderful HP41c, and waiting for a customer. This is the last I'll create in a lot of time!

Monte has not decided yet if to produce more boards, and if so, which changes from V4.

Let's now consider the most typical case of them: the calculator is for a student.

I hold the strong opinion that children should not use calculators until they master mental and written basica calculation: adding, subtracting, multiplying and dividing. That implies that they shouls have their first calculator around 12 years old. If they get to know that learning claculatin is not necessary, they will never do it. Your opinion may be different on this, but I think that there has to be a lower age limit.

After that limit, then there are two HP models that can be used: the HP10s+ and HP300s+. The difference between both is not substantial. Price is quite different, but none of them will break the bank. These can work until 14 years old.

Then, you need to do some investigation. Does his school support a particular calculator model? The school might support either a scientific calculator or a graphical calculator. 

If the school supports scientific calculators, he will be extremely happy with the HP35s - probably the most beautiful calculator on sale now. It looks professional, and all his companions will admire him for it. It doesn't make any sense to endow him with a HP15c or 42s - he will not appreciate it, and more important, his companions will not appreciate it either. Peer opinion is extremely important at that age.

If the school supports graphical calculators, then you really don't have any options. The HP50g is more aimed to university technical studies, and is on its way out. And your student will never forgive you if you give him the brick that the HP39gII is in comparison with the sleek Prime. so, the Prime has to be!

No student can be disappointed with a colour, tactile screen machine like the Prime. And it can do games too - but he'll have to learn some machine internals to play them - which is good, too.